Juste quelques améliorations au niveau des nommages

number_to_english_2.rb

# Il vaut mieux définir des constantes (aka des variables qui ne changerons jamais)
# en dehors de la méthode. Les constantes sont juste nomées en majuscule
#
# La syntaxe avec le `%w[]` permet simplement de définir des tableaux en mode un peu plus sexy
NUMBER_TRANSLATIONS = %w[one two three four five six seven eight nine].freeze
DOZEN_TRANSLATIONS = %w[ten twenty thirty forty fifty sixty seventy eighty ninety].freeze
TEENAGERS = %w[eleven twelve thirteen fourteen fifteen sixteen seventeen eighteen nineteen].freeze

# Convert a number to a beautiful string
# @param [Integer] as a number
# @return [String] as a pretty formated number
def english_number(number)
  return 'Please enter a number that isn\'t negative.' if number < 0 # No negative numbers.
  return 'zero' if number == 0

  # The string we will return.
  num_string = ''

  # how much of the number we still have left to write out.
  rest_number  = number
  # How many hundreds left to write out?
  number_of_hundred = rest_number / 100
  # Subtract off those hundreds.
  rest_number -= number_of_hundred * 100

  if number_of_hundred > 0
    # Now here's a really sly trick:
    hundreds  = english_number number_of_hundred
    num_string = num_string + hundreds + ' hundred'
    # That's called "recursion". So what did I just do?
    # I told this method to call itself, but with "write" instead of
    # "number". Remember that "write" is (at the moment) the number of
    # hundreds we have to write out. After we add "hundreds" to
    # "num_string", we add the string ' hundred' after it.
    # So, for example, if we originally called english_number with
    # 1999 (so "number" = 1999), then at this point "write" would
    # be 19, and "left" would be 99. The laziest thing to do at this
    # point is to have english_number write out the 'nineteen' for us,
    # then we write out ' hundred', and then the rest of
    # english_number writes out 'ninety-nine'.

    if rest_number > 0
      # So we don't write 'two hundredfifty-one'...
      num_string += ' '
    end
  end

  number_of_tens = rest_number / 10 # How many tens left to write out?
  rest_number -= number_of_tens * 10 # Subtract off those tens.

  if number_of_tens > 0
    if (number_of_tens == 1) && (rest_number > 0)
      # Since we can't write "tenty-two" instead of "twelve",
      # we have to make a special exception for these.
      num_string += TEENAGERS[rest_number - 1]
      # The "-1" is because TEENAGERS[3] is 'fourteen', not 'thirteen'.

      # Since we took care of the digit in the ones place already,
      # we have nothing left to write.
      rest_number = 0
    else
      num_string += DOZEN_TRANSLATIONS[number_of_tens - 1]
      # The "-1" is because DOZEN_TRANSLATIONS[3] is 'forty', not 'thirty'.
    end

    if rest_number > 0
      # So we don't write 'sixtyfour'...
      num_string += '-'
    end
  end

  if rest_number > 0
    num_string += NUMBER_TRANSLATIONS[rest_number - 1]
    # The "-1" is because NUMBER_TRANSLATIONS[3] is 'four', not 'three'.
  end

  # Now we just return "num_string"...
  num_string
end

puts 'Plz enter a number'
user_input = gets.to_i
puts english_number user_input